Modelling the ultrasonically assisted turning of high-strength alloys.

The thesis deals with a novel machining technique - ultrasonically assisted turning (VAT)·- and its comparison with conventional turning (CT). The main objective of the research is a detailed analysis of various features of both processes, especially the deformational and thermomechanical behaviour of the treated material. The main emphasis here is on the superalloy Inconel 718 due to the industrial demand. A thorough analysis of the cutting techniques is possible only with the use of advanced finite-element numerical simulations validated by a range of experimental methods (mechanical, optical, microstructural and thermal). Various effects of technological parameters (lubrication, thermal contact conditions, etc.) on deformational processes, stresses and chip formation are studied. High-speed filming of the cutter - workpiece interaction zone is conducted to compare chip formation processes for both technologies. Light microscopy, scanning electron microscopy (SEM) and nanoindentation analyses are employed to study the differences in the microstructure of surface layers of machined workpieces. Cuttingforce measurements and infrared thermography when turning with and without ultrasonic assistance are also carried out. The two-dimensional finite-element (FE) model is developed with MSC MARC general FE code and provides a transient, fully coupled thermomechanical analysis of both ultrasonic and conventional turning ofInconel 718. A detailed study of the VAT process is performed, including specificity of the single cycle of ultrasonic vibration. Differences between thermal and deformation processes for VAT and CT, effects of application coolant/lubricant, various friction conditions, and specific features of the heat conduction between chip and cutting tool are examined. For the first time, thermomechanics of VAT has been thoroughly analysed. The main outcome of the thesis is an in-depth understanding of the VAT process, and of its advantages and disadvantages in comparison to CT. Recommendations on further research development are also suggested.